(1) Field of the Invention
The present invention relates to a bidirectional DC-DC converter having an isolation function. The present invention also relates to a method for controlling the bidirectional DC-DC converter.
(2) Description of the Related Art
In recent years, increased use of highly efficient hybrid vehicles is promoted due to a rising demand for global environment conservation. The hybrid vehicles have a main battery for driving a traction motor and an auxiliary battery for driving accessories. The degree of freedom in designing a vehicle power supply system can be increased when the two batteries, which differ in voltage, are flexibly used for effective electrical power distribution.
In view of the above circumstances, a bidirectional DC-DC converter disclosed in JP-A No. 2002-165448 provides bidirectional electrical power conversion between two power supplies that differ in voltage. This converter is configured so that a high-voltage circuit is connected to a low-voltage circuit through a transformer. Operating a switching device in the high-voltage circuit supplies electrical power from a high-voltage power supply to a low-voltage power supply. Operating a switching device in the low-voltage circuit supplies electrical power from the low-voltage power supply to the high-voltage power supply.
A bidirectional DC-DC converter disclosed in JP-A No. 2006-187147 is configured so that a low-voltage circuit is connected to a voltage clamp circuit, which includes a series connection between a switching device and a capacitor. This converter uses the voltage clamp circuit to reduce a circulating-current-induced loss during a voltage decrease. Further, this converter makes it possible to decrease the dielectric strength of the switching device by suppressing the occurrence of a surge voltage in the low-voltage circuit during a voltage increase/decrease, and serves as a highly efficient, small-size, bidirectional DC-DC converter.
A bidirectional DC-DC converter disclosed in JP-A No. 2004-282828 is configured so that an LC resonant circuit is connected in series with a transformer winding. This converter exhibits low switching loss, makes it possible to eliminate the possibility of a large current flowing to a switching device upon power on/off, and serves as a bidirectional DC-DC converter that efficiently provides flexible electrical power distribution between two DC power supply systems through the use of a simple control scheme.